This proposal requests renewal of core funding for the Mexican Migration Project (MMP), whose purpose is to provide timely, reliable, high-quality data on documented and undocumented migrants from Mexico to the United States. The MMP fulfills a need for ongoing data on Mexican immigration that other potential sources are unable to meet. Over the past 15 years, the MMP has provided crucial data to numerous federal agencies and academic researchers to study the process of Mexico-U.S. migration, and project investigators have themselves made significant contributions to the research literature. Requested funds will go toward maintaining and improving the MMP website as the principal means of data dissemination and will enable the gathering new community samples for expansion of the data base. Sampling will focus on Mexico's central region, which in the past decade has emerged as a major new source for migrants to the United States. Research will attempt to deepen theoretical understanding of international migration by specifying the circumstances under which different theories come into play.